This invention relates to plasma reactor apparatus and, in particular, to a new structure for the control of gas flow within the reactor.
As known in the art, a considerable variety exists among the plasma reactors used in the semiconductor industry, e.g. for etching semiconductor wafers. There are what are known as barrel reactors, multi-electrode reactors, and parallel plate reactors. Each has its own characteristics, even when running what may arguably be the same process.
Parallel plate reactors usually process a single wafer at a time. While seemingly slower than batch operations in a barrel reactor, actual throughput is not actually very different since process rates tend to be higher in a parallel plate reactor. The major advantage of parallel plate reactors lies in the greater control of the process which this apparatus enables. Even among parallel plate reactors there are differences. One such difference is the manner in which reactant gases are supplied to the wafer.
In a first technique, gas is supplied to the wafer from a single port positioned above the central portion of the wafer. Gas and by-products are collected about the periphery of the wafer. Hence this reactor is often referred to a a radial flow reactor.
In a second technique, gas is supplied and exhausted from a plurality of ports located over the face of the upper electrode. This "spray nozzle" design seeks to avoid the dead spot which may form in the center of the wafer, directly under the pas ports resulting in an center-to-edge clearing pattern.
While each of these techniques is effective, there is a continuing need for ever greater uniformity across the surface of the wafer. As is known, the etch characteristics of some materials depends more on the electrical characteristics of the plasma than on the supply of gases. For example, polycrystalline silicon ("poly") is not particularly dependent on gas flow for etch uniformity. Poly has an ion bombardment limited etch. On the other hand, the etching of aluminum is sensitive to the supply of gases. This is not to say that the electrical characteristics of the plasma do not matter, only that gas flow has a more significant effect on the uniformity of the etch in the case of aluminum.
Thus, while all processes can benefit from improved uniformity, the present invention is especially useful for those processes which are reactant dependent. This is not to say that the supply of gas is particularly uniform, at least at any given time. Rather the present invention is directed to providing superior control within a plasma reactor in order to accommodate other changes which may be made and which would normally upset the process being run.
It is desired to have plasma reactors capable of accommodating various processes and wafer sizes without having to have a separate reactor for each. For example, changing wafer size changes the "loading" of the chamber. Process parameters must be modified to accommodate the change or the process is useless. Until now, it has been difficult to accommodate the change, particular in radial flow reactors, particularly as wafer sizes increase.
In view of the foregoing, it is therefore an object of the present invention to provide improved gas flow control for plasma reactors.
Another object of the present invention is to provide means for controlling the flow of gases within a plasma reactor so that changes in process or dimensions can be accommodated.
A further object of the present invention is to obtain improved uniformity from plasma processes.
Another object of the present invention is to reduce the edge-to-center clearing pattern of radial flow reactors.